Synthetic aircraft turbine oil

ABSTRACT

Synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and an organic monocarboxylic acid containing (a) from about 0.005 to 0.5 percent of a thiouracil compound, (b) from about 0.3 to 5 percent of an alkyl or alkaryl phenylnaphthylamine; (c) from about 0.3 to 5 percent of a dialkyldiphenylamine; and (d) from about 0.25 to 10 percent of a hydrocarbyl phosphate ester.

United States Patent 11 1 [111 3,901,815

Reale, Jr. 1 Aug. 26, 1975 [54] SYNTHETIC AIRCRAFT TURBINE OIL 3,779,921 12/1973 Patmore et a], 252/475 X 3,798 164 3/1974 Kmet eta]. 252/475 [75 lnventor: John Reale, Jr., Wappmgers Falls,

Primary Examiner-Delbert E. Gantz 173 l Assignee: Texaco Inc.. New York. NY. Assistant Examiner-Andrew H. Metz Attorney, Agent, or Firm-T. I-I. Whaley; C. G. Ries; [22] Fil i J n 1 James J. OLoughlin [21] Appl. No.: 476,625

[57] ABSTRACT [52] CL 252/46'7: 252/475 52 35 6 Synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having 1n- [51] Int. Cl CIOm 1/48 f d f th f Field 0 Search 252/46 7 47 5 ricatlng proper res orme rom e reac ion 0 a pentaerythntol or trimethylolpropane and an organlc monocarboxylic acid containing (a) from about 0.005 [56] References cued to 0.5 percent of a thiouracil compound, (b) from UNITED STATES PATENTS about 0.3 to 5 percent of an alkyl or alkaryl phenyl- 2.800,491 7/1957 Ellis 252/475 X naphthylamine; (c) from about 0.3 to 5 percent of a 9 3/1960 Tifimey 6131- dialkyldiphenylamine; and (d) from about 0.25 to 10 3,404,090 10/1968 Betty a a1. 252/475 percent f a hydrocarbw phosphate esten 3,476,685 11/1969 Oberender et al 252/467 3,553,131 1/1971 Hepplewhite et a1 252/467 9 Claims, No Drawings SYNTHETIC AIRCRAFT TURBINE OIL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is concerned with the lubricating oil 5 composition used in gas turbine or jet engines. Gas turbine engines are operated under extreme environmental conditions. The lubricant must be fluid at extremely low temperatures and must be an effective lubricant in an engine which produces internal engine temperatures in the range of 450500F. or above. These operating conditions put severe stresses on the lubricating oil, so much so that the most advanced mineral lubricating oil compositions cannot be employed in gas turbine engines.

Currently, synthetic ester base lubricating oil compositions containing a critically balanced blend of additives are being effectively employed for lubricating gas turbine engines. These ester base oils are operative over a wide temperature range and exhibit high thermal stability, anti-wear, load-carrying and antioxidation properties while providing good lubrication.-

With the advent of newer and more powerful gas turbine engines designed to provide advanced levels of supersonic flight, the resulting higher stress levels require lubricating oil compositions having improved loadcarrying properties.

2. Description of the Prior Art No patents are known which disclose thiouracils or their salts as load-carrying additives for synthetic ester base lubricating oil composition.

SUMMARY OF THE INVENTION The synthetic lubricating oil composition of the invention comprises a major portion of an aliphatic ester base oil having lubricating properties containing a thiouracil compound, an alkylphenyl or alkarylphenyl naphthylamine, a dialkyldiphenylamine, and a hydrocarbyl phosphate. More specifically, the lubricating oil composition of the invention comprises a major portion of an aliphatic ester base oil formed from the reaction of a pentaerythritol or trimethylolpropane and an organic monocarboxylic acid having from about 2 to l8 carbon atoms per molecule containing:

a. from about 0.005 to 0.5 weight percent of a thiouracil compound selected from the class of thiouracils, dithiouracils and their amine salts.

b. from about 0.3 to 5 percent by weight of the lubrieating oil composition of allkyl or alkaryl derivatives of 50 phenyl or or B naphthylamines in which the alkyl radicals have from four to 12 carbon atoms.

0. from about 0.3 to 5 percent of a dialkyldiphenylamine in which the alkyl radicals have from four to 12 carbon atoms, and

d. from about 0.25 to l0 percent of a trihydrocarbyl phosphate in which the hydrocarbyl radicals contain from about two to 12 carbon atoms.

The lubricating oil of the invention is characterized by possessing outstanding load-carrying properties. These properties are attributed to a carefully balanced and formulated synthetic ester base lubricating oil blend containing a thiouracil compound. The results were surprising and unexpected because heretofore thiouracil compounds have not been known to impart load-carrying properties to a synthetic ester lubricating oil composition.

The base fluid component of the lubricant of the invention is an ester-base fluid prepared from pentaerythritol or trimethylolpropane and a mixture of hydrocarbyl monocarboxylic acids. Polypentaerythritols, such as dipentaerythritol, tripentaerythritol and tetrapentaerythritol can also be employed in the reaction to prepare the base oil.

The hydrocarbon monocarboxylic acids which are used to form the ester-base fluid include the straightchain and branched-chain aliphatic acids, cycloaliphatic acids and aromatic acids as well as mixtures of these acids. The acids employed have from about two to 18 carbon atoms per molecule, and preferably from about five to 10 carbon atoms. Examples of suitable specific acids are acetic, propionic, butyric, valeric, isovaleric, caproic, decanoic, hexadecanoic, vinylbenzoic, dodecylbenzoic, pelargonic, cyclohexanoic, naphthenic, benzoic, phenylacetic, tertiary-butylacetic and 2-ethylhexanoic acids.

In general, the acids are reacted in proportions leading to a completely esterified pentaerythritol or trimethylolpropane with the preferred ester base being the pentaerythritol tetraesters. Examples of commercially available tetresters include pentaerythritol tetracaproate, which is prepared from purified pentaerythritol and crude caproic acid containing other C monobasic acids. Another suitable tetraester is prepared from a technical grade pentaerythritol and a mixture of acids comprising 38 percent valeric, l3 percent 2-methyl pentanoic, 32 percent octanoic and 17 percent pelargonic acids. Another effective ester is the triester of trimethylolpropane in which the trimethylolpropane is esterified with a monobasic acid mixture consisting of 2 percent valeric, 9 percent caproic, 13 percent heptanoic, 7 percent octanoic, 3 percent caprylic, 65 percent palargonic and 1 percent capric acids. Trimethylolpropane triheptanoate, trimethylolpropanepentanoate and trimethylolpropanehexanoate are also suitable ester bases.

The ester base comprises the major portion of the fully formulated synthetic ester base lubricating oil composition. In general, this ester base fluid is present in concentrations from about to 98 percent of the composition.

The essential thiouracil compound is selected from the group consisting of the thiouracils, dithiouracils and the amine salts of these compounds.

The thiouracils are represented by the formula:

in which R is hydrogen or a hydrocarbyl radical having from one to about 30 carbon atoms. A preferred class of compounds are those in which R is hydrogen, an alky], aryl, or alkaryl radical having from one to about eight carbon atoms and particularly from one to six carbon atoms.

The dithiouracils are represented by the formula:

in which R has the values noted above.

The amine salt of a thiouracil compound is represented by the formula:

c=c -s-c \N Y in which R has the values noted above and Y represents hydrogen or an ammonium radical represented by the formula H NR in which R is a hydrocarbyl radical having from one to 24 carbon atoms, at least one Y member being said ammonium radical.

Specific examples of effective thiouracil compounds include the following:

2-thiouracil tS-methyl Z-thiouracil fi-elhyl 2 thiouracil 6-propyl Z-thiouracil o-phenyl 2 thiouracil b-benzyl Z-Ihiouracil 5.6-dimethyl 2-thiouracil 5 ,fi-diphenyl 2thiouracil 6-( 4-isopropylphenyl Z-thiouracil Specific examples of dithiouracil compounds include the following:

2,4dithiouracil fi-methyl 2,4-dithiouracil 6-ethyl 2,4-dithiouracil 6propyl 2,4-dithiouracil 6-phenyl 2,4-dithiouracil 6 benzyl 2,4dithiouracil 5,6-dimethyl 2.4-dithiouracil 5,6-diphenyl 2,4-difl1iouracil 65 about 0.005 to 0.5 weight percent with the preferred concentration ranging from about 0.0l to 0.1 weight percent.

The essential alkyl or alkaryl phenyl naphthylamine component of the invention is represented by the formula:

in which R is an alkyl or alkaryl radical having from about three to 12 carbon atoms. This radical can be a straight or branched chain alkyl radical with the tertiary alkyl structure being preferred or it can be an alkaryl radical. The naphthylamine can be either an alpha or beta naphthylamine. Specific effective compounds of this class include N-(p-t-octylphenyDanaphthylamine. N-( p-a-cumylphenyl )-6-a-cumyl-B- naphthylamine, N(p-t-octylphenyl)-B-naphthylamine and the corresponding p-t-dodecylphenyl, p-tbutylphenyl, and p-dodeeylphenyl-o: and -B-naphthy1 amines. The preferred concentration of this component is from about 0.5 to 2.5 percent.

Another essential component of the lubricating oil composition of the invention is a dialkyldiphenylamine. These compounds are represented by the formula:

in which R is an alkyl radical having from about four to 12 carbon atoms. Suitable alkylamines include dioctyldiphenylamine, didecyldiphenylamine, didodecyldiphenylamine, dihexyldiphenylamine and similar compounds. The preferred compound is p,p'-di-toctyldiphenylamine and the preferred concentration isfrom 0.5 to 2.0 percent.

The final essential component of the lubricating oil composition of the invention is a hydrocarbylphosphate ester. more specifically a trihydrocarbyl phosphate having the formula (RO) PO in which R is a hydrocarbyl radical i.e. an alkyl, aryl, alkaryl, cycloalkyl or aralkyl radical or mixture thereof having from two to 12 carbon atoms and preferably from four to eight carbon atoms. Effective specific compounds include tricresylphosphate, cresyl diphenylphosphate, triphenylphosphate, tributylphosphate, tri( 2-ethylhexyl)- phosphate and tricyclohexyl phosphate. These compounds are preferably present in the lubricating oil composition in a concentration ranging from about 0.5 to 5 percent.

The lubricating oil composition of the invention was tested for its load-carrying property in the [AB Gear Test conducted in accordance with the institute of Fetroleum Test Method lPl66" and the Ryder Gear Test conducted in accordance with the ASTM Dl947 standard.

The ester base oils employed in preparing the lubricating oil compositions tested below comprised pentaerythritol containing a minor amount of dipentaerythritol esterified with mixtures of fatty acids.

Base Oil A consisted of technical grade pentaerythritol ester made from a mixture of carboxylic acids consisting of (mole 96):

This ester base oil had the following properties:

Viscosity, on at 2l0'F. 5.03 Viscosity, cs at lF. 25.l Viscosity, cl at 40F. 7247 Viscosity Index 140 Flalh, 'F. 490

TABLE I EVALUATION OF THIOURACIL COMPOUNDS LOAD-CARRYING ABILITY Conc. IAE GEAR RYDER GEAR Run Additive Wt.% TEST, l l0C TEST ppi 6000 rpm 1. None 40 2055 2. Dithiour- 0.085 55 3025 acil 3. C -C 0.5 3075 alkylprimary amine salt of dithiouracil 4. 2-thiour- 0.05 2340 acil The novel synthetic ester base lubricant of the invention containing a thiouracil compound possesses outstanding load-carrying properties as shown in the lAE Gear and the Ryder Gear Tests above. These lubricants are highly effective for providing a synthetic lubricating oil composition which can meet the ever increasing stresses put on the lubricants by the new and larger gas turbine engines.

l claim:

1. A synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and a saturated hydrocarbyl monocarboxylic acid having from about 2 to 18 carbon atoms per moledule, containing A. From about 0.005 to 0.5 weight percent of a thiouracil compound represented by the formula selected from the group consisting of I l c c m t 2 l'lll i l c 0 (ii! 5 (2/ Nil d I II /c c um -s C Y2 wherein R is hydrogen or a hydrocarbyl radical having from one to about 30 carbon atoms and Y is hydrogen or an ammonium radical having the formula H NR' in which R is a hydrocarbyl radical having from one to 24 carbon atoms, at least one Y being said ammonium radical.

8. From about 0.3 to 5 percent by weight of the lubricating oil composition of an alkyl or alkaryl phenyl naphthylamine in which the alkyl radical has from three to 12 carbon atoms,

C. From about 0.3 to 5 percent of a dialkyldiphenylamine in which the alkyl radicals have from four to 12 carbon atoms, and

D. From about 0.25 to 10 percent of a trihydrocarbyl phosphate in which said hydrocarbyl radicals contain from about two to 12 carbon atoms.

2. A lubricating oil composition according to claim 1 in which said thiouracil compound is a thiouracil represented by the formula:

in which R is hydrogen or a hydrocarbyl radical having from one to about 30 carbon atoms.

3. A lubricating oil composition according to claim 1 in which said thiouracil compound is a dithiouracil represented by the fon'nula:

in which R is hydrogen or a hydrocarbyl radical having from one to about 30 carbon atoms.

in which R is hydrogen or a hydrocarbyl radical having from one to about 30 carbon atoms, and Y is hydrogen or an ammonium radical having the formula H NR in which R is a hydrocarbyl radical having from one to 24 carbon atoms, at least one Y member being said ammonium radical 5. A lubricating oil composition according to claim 1 in which said thiouracil compound is dithiouracil.

6. A lubricating oil composition according to claim 1 in which said thiouracil compound is C -C -t-alkyl primary amine salt of dithiouracil.

7. A lubricating oil composition according to claim 1 in which saidthiouracil compound is 2-thiouracil.

8. A lubricating oil composition according to claim 1 in which said thiouracil compound is 6-methyl-2- thiouracil.

9. A lubricating oil composition according to claim 1 in which said thiouracil compound is 2-ethylhexylamine salt of 2,4-dithiouracil. 

1. A SYNTHATIC LUBERCATING OIL COMPOSITION COMPRISING A MAJOR PORTION OF AN ALIPHATIC ESTER BASE OIL HAVING LUBERCATING PROPERTIES FORMED FROM THE REACTION OF A PENTAERYTHRITOL OF TRIMETHYLOPROPANE AND A SATURATED HYDROCARBYL MONOCARBOXYLIC ACID HAVING FROM ABOUT 2 TO 18 CARBON TOMS PER MOLEDULE, CONTAINING A. FROM ABOUT 0.005 TO 0.5 WEIGHT PERCENT OF A THIOURACIL COMPOUND REPRESENTED BY THE FORMULA SELECTED FROM THE GROUP CONTAINING OF
 2. A lubricating oil composition according to claim 1 in which said thiouracil compound is a thiouracil represented by the formula:
 3. A lubricating oil composition according to claim 1 in which said thiouracil compound is a dithiouracil represented by the formula:
 4. A lubricating oil composition according to claim 1 containing the amine salt of said thiouracil compound represented by the formula:
 5. A lubricating oil composition according to claim 1 in which said thiouracil compound is dithiouracil.
 6. A lubricating oil composition according to claim 1 in which said thiouracil compound is C18-C22 -t-alkyl primary amine salt of dithiouracil.
 7. A lubricating oil composition according to claim 1 in which said thiouracil compound is 2-thiouracil.
 8. A lubricating oil composition according to claim 1 in which said thiouracil compound is 6-methyl-2-thiouracil.
 9. A lubricating oil composition according to claim 1 in which said thiouracil compound is 2-ethylhexyl-amine salt of 2,4-dithiouracil. 